Liquid paper containers for food and non-food liquid content, typically milk, are widely used. These containers use paper as a base material and made of a laminate in which a thermoplastic resin sealant layer is provided on an inner surface thereof. Liquid paper containers are also widely used for liquid food products such as fruit and other kinds of juice beverages, tea, coffee, milk, and soup, and alcoholic beverages such as sake (rice wine) and shochu (distilled spirit).
Some of these liquid paper containers are constituted by a paper base material and a sealant layer, but others have a gas barrier layer by use of an aluminum foil, a metal-deposited film, a metal-oxide-deposited film or other types between the paper layer and the sealant layer, or have a layer with gas barrier properties, such as an inorganic-compound-deposited film (see, for example, PTL 1).
Paper containers are widely used by virtue of their convenience and economy, and are common as packaging containers for various products. In recent years, containers are required to be less voluminous when they are disposed of from the viewpoint of environmental conservation. In addition, there is a change in consumers' awareness, as demonstrated by the fact that a mechanism for recycling the containers as a resource is being established. Under such circumstances, for example, used milk cartons are disassembled by consumers for recycling before being placed on a sorting collection route. In addition, even containers that are not collected for recycling are often disassembled and made less voluminous before being disposed of.
However, there is a problem at a time of actual disassembly of the containers. For a liquid paper container provided with a spout on the roof plate of a gable-roof-shaped top part, for example, there is practically no other choice but to open the top sealing part and cut around the spout with scissors or the like to take the spout off for disposal because the spout is firmly welded.
Furthermore, in the conventional liquid paper container described above, the top sealing part is firmly sealed by thermal fusion, which on occasions forces people to struggle to open the top sealing part by hand to disassemble the container after the container is emptied.
This is because the top sealing part of the liquid paper container is sealed with a bent laminate being abutted, which is likely to allow a gap, so that a highly flowable polyethylene resin is used on a sealant layer on the rear surface of the liquid paper container and sealed with a high temperature and a strong pressing force so as to fill and completely seal the gap.
Such circumstances are the reasons for the firm sealing. Lowering the sealing temperature or weakening the pressing pressure to reduce the sealing strength may possibly result in incomplete sealing, which may in turn cause a liquid leakage.
Rather than opening the top sealing part, cutting an opening of a spout with scissors can also disassemble an empty container, but cutting a hard spout or its surroundings with scissors accompanies significant trouble and is cumbersome because the method requires a tool, and therefore are not practiced commonly.
An improvement to this situation is a liquid paper container that allows a side plate of the body part thereof to be cut and torn to trigger easy disassembly.
For example, PTL 2 discloses a liquid paper container where both ends of a composite sheet provided with a synthetic resin layer on the front and rear sides of a paper layer are overlapped with each other, and a pull tab is provided at an end of the composite sheet on the outer surface side of a sealed part for bonding the body part, the pull tab being peelably provided via a peeling layer of a easily peelable tape-like film. This tape-like film is provided continuously along an inner surface of a four-side surface plate, and has a cutting line, such as a cut line, a half cut line, and a perforated line, engraved on a paper layer of the composite sheet along both widthwise edges of the tape-like film.
This proposed liquid paper container in PTL 2, however, requires an easily peelable tape-like film and poses a risk that the sealing on the body sealing of the part for bonding the body part weakens due to the peelability of the tape-like film. Thus there is a demand for further improvement in ease of disassembly of a used container or for another method that simplifies disassembling thereof.